1. Technical Field
The present invention relates to a position adjustment method for projection images used in a multi-projection display which produces a picture by projecting images from a plurality of projectors onto a projection surface, a position adjustment apparatus for projection images, a position adjustment program for projection images, and a multi-projection display.
2. Related Art
Currently, a multi-projection display which projects images from a plurality of projectors onto a projection surface by tiling projection or stacking projection is known. According to the multi-projection display, the accuracy of position adjustment for the respective projection images on the projection surface has a great effect on the quality of the projection images.
In a case of the tiling projection, for example, low accuracy of position adjustment causes considerable deterioration of the projection image quality such as discontinuous joints between the respective projection images and blurs in the overlapping areas.
To overcome this drawback, position adjustment for the respective projection images is essential, but this requires great time and labor and also high-level position adjustment technique when the position adjustment is manually performed by a user.
Accordingly, various methods for automatically executing position adjustment have been proposed (for example, see JP-A-2001-356005 and JP-A-2002-365718).
According to the technique shown in JP-A-2001-356005, a plurality of test pattern images (which exhibit luminance distributions having mountain-shaped waveforms) projected on a projection surface are taken by a camera to obtain the respective typical positions (central positions of mountain-shaped waveforms) of the plural test patterns from the taken image data. Then, based on the respective typical positions thus obtained, the distances between the respective test pattern images and the distances between the cross points of the line segments connecting the test pattern images and the adjoining pictures in both or either of the horizontal direction and the vertical direction are obtained so as to determine positional displacement based on those distances.
According to the technique disclosed in JP-A-2002-365718, two adjustment patterns each having a black portion along the boundary between adjoining projection images and a white portion located inside the black portion are displayed by two projectors to show a dark line on the overlapping area. Then, the image of the black portion is taken by an image taking device while gradually decreasing the width of the black portion. Subsequently, the width changes of the dark line are observed based on the image data thus taken and the position at which the dark line disappears is stored as a boundary position. Thereafter, position adjustment is conducted such that the contours of the projection images coming from the respective projection devices coincide with the boundary position.
In both the techniques shown in JP-A-2001-356005 and JP-A-2002-365718, adjustment images are projected on the projection surface using two projectors and then are taken by the image taking device so as to perform position adjustment based on the image data thus taken.
According to the technique disclosed in JP-A-2001-356005, displacement can be detected using an image taking device having lower resolution than that of the projection images. However, since complicated image analysis processing is required for displacement detection, an image data processing device having sufficiently high processing performance is needed. Also, since the calculation volume is large, processes required for correcting displacement cannot be carried out at high speed.
According to the technique shown in JP-A-2002-365718, an image taking device having high resolution sufficient for resolving the projection images by pixel is required to obtain the boundary position with high accuracy.
Moreover, when position adjustment is performed using the methods disclosed in JP-A-2001-356005 and JP-A-2002-365718, it is necessary to consider the effect of the illumination condition inside a room where the position adjustment is conducted or in other environment given to the image taking device. This is because appropriate position adjustment cannot be achieved in many cases based on image data each obtained under the environment of different illumination conditions. In an extremely dark environment having no illumination such as a darkroom, for example, the effect of some inhibiting factors which are ignorable under the illumination condition of normal brightness increases and thus prevents achievement of appropriate position adjustment. Examples of the inhibiting factors include the color array structure of color filters used in a single-plate-type image taking device, for example, which will be described later.
Thus, in a case of position adjustment in the extremely dark environment such as a darkroom, consideration for the effect of the inhibiting factors is essential. However, no such consideration is especially discussed for the techniques of JP-A-2001-356005 and JP-A-2002-365718 .